Context

This MR updates the minimal_block_delay to 20 seconds. It also updates the related constants.

This MR is currently delayed until more confidence is gained (for instance by resilience testing).

Manually testing the MR

The CI should suffice for a first check.

Stress tests and a testnet should be run to confirm that all this is ok.

[N/A] Document the interface of any function added or modified (see the coding guidelines)
[N/A] Document any change to the user interface, including configuration parameters (see node configuration)
[N/A] Provide automatic testing (see the testing guide).
For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, the Development Version section of CHANGES.md for everything else).
Select suitable reviewers using the Reviewers field below.
Select as Assignee the next person who should take action on that MR

Edited Feb 24, 2022 by Eugen Zalinescu